We have constructed a recombinant plasmid (pA28) in which the transcription of the v-mos gene can be induced under the control of lambda pL promoter to amplify the v-mos gene product to greater than 5% of the total cellular protein. This was accomplished by inserting the entire v-mos gene of Mo-Murine Sarcoma virus (HT-1) at cla I site of pJL6, a plasmid vector that contains lambda pL promoter and sequences coding for NH2-terminal portion of the lambda cII gene. In the resulting plasmid (pA28) the transcription begins at lambda pL promoter and the translation initiates at ATG of the lambda cII gene and terminates at TGA of v-mos to yield a predicted cII-mos hybrid protein. SDS-gel electrophoresis of the total cellular proteins indicates that the fusion is a polypeptide of molecular weight (MW) 41,000 daltons.